Determine a definition for matter based on mass measurement and volume occupied by that mass. Define a substance and extend the definition to define a pure substance. Relate uniform and unchanging composition. Use a mix of iron filings and sulfur powder as a mix of two pure substances and define them as a mixture. Note that each retains its own individual properties, e.g. magnetism for iron. Determine that substances can be separated by physical means. Use example of silver and mercury used in tooth filings. They can be separated by temperature of evaporation.